1. Field of the Invention
The present invention relates to a polishing pad for polishing the surfaces of objects such as semiconductors, storage medium substrates, integrated circuits and electro-optical panels, and relates to a method for making the polishing pad.
2. Related Prior Art
In the semiconductor industry, there is a trend toward the reduction of the semiconductor characteristics and the increasing of the superficial planarity. In detail, it is preferred to provide a surface with an even form by reducing the quantity and size of superficial flaws.
Polishing is often used to turn a rough surface into a smooth surface. Amid other polishing methods, there are fixed-type polishing methods and suspension-type polishing methods.
In a fixed-type polishing method, used is a fixed-type polishing pad with a polishing layer on a substrate. The substrate is a PET foil for example. The polishing layer includes polishing particles and an adhesive for fixing the polishing particles to the substrate. Although providing a high polishing rate, the fixed-type polishing pad causes grave impacts on the polished surface, and it is difficult to clean the polished surface of debris. Hence, many large and deep scratches are made in the polished surface, and this is not desirable.
In a suspension-type polishing method, used is a suspension-type polishing pad with a polishing solution on a substrate. The polishing solution is a suspension with polishing particles suspended in a solvent. For the use of the solvent, it is easy to clean the polished surface of debris. As suspended in the solvent, the polishing particles freely move. Hence, the impacts on the polished surface by the suspended polishing particles can readily be adjusted. Moreover, it is easy to control the result by changing the suspension-type polishing pad. Various velvets and fabrics are used in the suspension-type polishing pad to achieve adequate effects according to different purposes.
In the suspension-type polishing method, the polishing solution is provided between the substrate and the polished surface, and the substrate is regularly rotated related to the polished surface. The substrate of the suspension-type polishing pad may include urethane or polyurethane plastics filled in a blanket made of polyester. Alternatively, the blanket may be made of natural fibers such as wool.
Chemical mechanical polishing (“CMP”) is often used in a typical machine for polishing semiconductor devices. In a CMP method, a polishing pad includes a polishing solution on a substrate. The polishing pad is used to polish the surfaces of semiconductor devices. The polishing solution is provided between a wafer and the substrate, and the wafer is pressed on and rotated relative to the polishing pad while chemical substances in the polishing solution and the pressure and rate between the wafer and the polishing pad and temperature are under control. The polishing solution includes polishing particles capable of mechanically polishing the surface of the wafer when mixed with the chemical substances. Between the chemical substances and the surface of the wafer, chemical reactions such as removal and oxidation happen. The polishing pad often includes a continuous substrate. When the wafer is rotated relative to the polishing pad, some redundant material is mechanically removed from the surface of the wafer by the polishing particles of the polishing liquid while some other redundant material is chemically removed from the surface of the wafer by the solvent of the polishing liquid.
Disclosed in US Patent Application Publication 2002/0013984A1 is a sheet for texturing and a method of producing the same. The method includes four steps among which the second and third steps can be interchanged.
Firstly, a non-woven fabric is composed of ultrafine fiber-generating fibers (a) and (b).
Secondly, an elastomer is filled in the non-woven fabric so as to form a sheet.
Thirdly, the ultrafine fiber-generating fibers (a) are converted to bundles of ultrafine fibers while the ultrafine fiber-generating fibers (b) are converted to bundles of ultrafine fibers not more than 0.03 dtex in fineness.
Fourthly, at least one side of the sheet is ground so that the ultrafine fibers under 0.03 dtex in fineness form nap.
A polishing layer is formed on the side of the sheet on which the nap is formed. However, in the step of converting the fibers (a) and (b) to the ultrafine fibers, since the polishing layer includes the polymer and the fibers, the polishing layer cannot adequately be opened so that the nap is not fine enough and that the nap may get entangled. If the polishing layer contains too much polymer, when it is used to polish an object, particles (polishing synthetic materials, sheet materials, polishing particles, particles of sheet materials and debris of the object) will stick to the polymer of the polishing layer and cannot smoothly be removed by a polishing solution. These redundant particles will wear away the object and jeopardize the polishing of the object.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art.